Metal ladders

ABSTRACT

A metal ladder, in which each stile has a pair of spaced parallel ribs on its inner and outer faces, and is formed with pairs of slots close to the ribs, and each rung has a cross section in the form of a hollow parallelogram, with two spaced parallel tabs projecting at each end. The tabs are inserted through the slots and crimped over the outer ribs, and the sidewalls of the rungs locate against the ribs on the inwardly facing surfaces of the stiles.

ijiie iaies ?atet Englhardt Feb. 1, W72

[54] METAL LADDERS 2,957,543 10/1960 Larson 1 82/228 [72] Inventor: Robe" Anton Englhardt Etobicoke 3,279,05l 10/1966 Minshall 1 82/228 Canada FORElGN PATENTS 0R APPLICATIONS [73] Canada Canada 497,082 3/1937 Great Britain ..1s2/22s [22] Filed: Mar. 30, 1970 Primary ExaminerReinaldo P. Machado [2]] Appl' 23738 Attorney0lson, Trexler, Wolters & Bushnell [30] Foreign Application Priority Data [57] ABSTRACT Jan. 16, Great Britain A metal ladder, in which each stile has a pair of spaced pa -a]- lel ribs on its inner and outer faces, and is formed with pairs of [52] [1.5. Ci ..182/194, 182/228 Slots close to the ribs, and each rung has a cross Section in the [51] 10 Cl. "E066 7/50 form of a hollow parallelogramy with two spaced parallel tabs Fleld 0f p j g at each end. The tabs are inserted through the Slots and crimped over the outer ribs, and the sidewalls of the rungs [56] References cued locate against the ribs on the inwardly facing surfaces of the UNITED STATES PATENTS Smas- 944,000 12/ 1909 Schoninch et al. 182/228 4 Claims, 6 Drawing Figures SHEET 1 OF 2 73\ 2 2 I III Fla. 3

NVENTOR ATTORNEYS.

PATENTEDFEB 11972 3.638.759

SHEET 2 OF 2 ATTORNEYS METAL LADDERS This invention relates to metal ladders and is particularly though not exclusively applicable to ladders in which the stiles and rungs are formed from light alloy extrusions.

Although the basic design of a ladder may be comparatively simple the detailed construction presents a number of problems. In particular there is a need for an effective joint between the ends of the rungs and the stiles which will hold the rungs securely to the stiles, prevent the rungs working loose or rotating, and yet be simple and economical to manufacture. Furthermore the complete ladder should have an attractive clean overall appearance and should be safe in use. For example when used at an inclination it is desirable that the top surfaces of the rungs should be approximately horizontal. Accordingly it is an object of the invention to provide a metal ladder with an improved joint construction between the rungs and stiles.

Broadly from one aspect the invention consists in a metal ladder including a pair of stiles and interconnecting rungs, in which each stile has a pair of spaced parallel ribs on the side thereof facing towards the other stile, and the rungs are of noncircular cross section with substantially flat opposed surfaces lying generally parallel with and in contact with, or closely adjacent to the respective ribs on the stiles.

Conveniently each rung is of hollow box section, having two further parallel generally flat upper and lower surfaces, and in a particular preferred construction the cross section of each rung is a parallelogram, with the top and bottom surfaces inclined to the side surfaces.

In any case the ribs of the stiles are preferably spaced inwardly from the edges thereof.

From another aspect the invention consists in a metal ladder including a pair of stiles, and interconnecting rungs, in which each stile has a pair of spaced ribs on its outer surface, and is formed with an elongated aperture adjacent each rib at the position of each rung, and each rung has a pair of tabs at each end which extend through the respective apertures and are bent back over the adjacent rib.

Preferably each rung is of hollow box section, with substantially flat opposed side surfaces, and the tabs are extensions of said side surfaces.

According to another aspect of the invention in a metal ladder having a pair of stiles and interconnecting rungs, each stile has a pair of spaced parallel ribs on both its inner and outer surfaces, preferably aligied with each other, and each rung has flat opposite side surfaces which abut against the inwardly facing ribs, and tabs which pass through apertures in the stiles and are bent over the outwardly facing ribs.

The invention may be performed in various ways and one specific embodiment will now be described by way of example with reference to the accompanying drawings, in which:

FIG. I is an end view of an extruded metal stile for a ladder according to the invention,

FIG. 2 is an inner side view of part of the stile of FIG. 1, showing in cross section a metal rung attached to the stile,

FIG. 3 is a sectional view through the stile on the line III-III in FIG. 2, showing the method of securing the end of a metal rung,

FIG. 4 is an outer side view of part of the stile showing the external view of the connection between the stile and the rung,

FIG. 5 is a perspective view of one end of a metal rung showing the preformed tabs used in making the connection, and

FIG. 6 is a general front elevation on a small scale ofa metal ladder according to the invention having rungs and stiles connected together in the manner illustrated.

In the example illustrated generally in FIG. 6 the ladder comprises a pair of elongated stiles I0, each formed as an aluminum alloy extrusion, and a series of interconnecting rungs I2 each of which is also a hollow box-section aluminum alloy extrusion.

Each stile comprises a generally flat web portion 13 (see FIG. 1), approximately 2% inches in width, with a relatively narrow perpendicular flange 14 at each edge. A pair of shallow spaced ribs 15 is provided on the inner face of the main web, and a further pair of spaced ribs 16 on the outer face, these ribs l5, 16 being aligned one with another and spaced apart across the web at an interval of approximately 1% inch. The section as described above is formed as an extrusion and in the subsequent manufacture of the ladder a pair of slots 17 are formed through the web at the position where each rung is to be joined, each slot having a length (parallel to the length of the stile) of approximately 1 inch and being positioned in the part of the web between the ribs 15, 16, and closely adjacent to and parallel with the ribs. For a reason which will become apparent the slot adjacent one edge of the web at each rung position is slightly above the level of the slot adjacent the other edge of the web.

Each rung 12 is of hollow box section, the actual section being a parallelogram (see FIG. 2) with a relative inclination of approximately 75 between the side, or vertical" surfaces 20, and the top and bottom surfaces 21, 22. The top surface 21 may be fluted or ribbed to provide an antislip tread. The perpendicular distance between the opposite side surfaces 20 is approximately 1% inch, i.e., slightly less than the interval between the pairs of ribs 15 on the inner surface of the stile. In the construction of a ladder each rung is first cut to a length slightly greater than the required perpendicular distance between the stiles l0 and each end of a rung is then trimmed by cutting out a short section of the upper and lower surfaces 21, 22, (see FIG. 5) leaving projecting tabs 24, 25, formed by the projecting parts of the side surfaces 20. These tabs can then be passed through the respective apertures I7 in the stiles, and the end of each tab is then turned outwards towards the adjacent edge of the web and tightly crimped over the respective rib 16 on the outer face of the web (see FIG. 3).

This provides a very simple and effective joint. Movement of the rung 12 relative to the stiles 10 is resisted both by the engagement of the rung side surfaces 20 with the inwardly facing ribs 15, and also by the tightly crimped engagement between the tabs 24, 25, and the outwardly facing ribs 16. The upper surface 21 of each rung is substantially flat, and being inclined slightly with respect to the stiles I0 will normally be approximately horizontal when the ladder is in use. The construction of the joint is extremely simple to perform and involves a minimum of operations on the stiles and rungs. The completed ladder construction is extremely clean and attractive in appearance.

In a possible modification (not illustrated) the ribs 15 on the adjacent or inwardly facing surfaces of the stile webs are omitted and the engagement between the tabs 24, 2S, and ribs 16 on the outer surfaces are relied upon to form the joint. In another possible alternative the ribs 16 on the outer surfaces of the stiles are omitted and the tabs 24, 25 on the rungs are simply curled or crimped over against the outer surface of the web 13, the rigidity of the joint being provided by the engagement of the rung surfaces 20 with the inwardly facing ribs 15 and the positioning of the tabs 24, 25 within the elongated slots 17 in the web. Preferably however the ribs 15, I6, are formed on both the inner and outer surfaces of each stile, as described above.

lclaim:

l. A metal ladder including a pair of stiles, and interconnecting rungs, in which each stile has a pair of spaced ribs on its outer surface, and is formed with an elongated aperture adjacent each rib at the position of each rung, and each rung has a pair of tabs at each end which extend through the respective apertures and are bent back over the adjacent rib.

2. A metal ladder according to claim 1, in which each rung is of hollow box section with substantially flat opposed side surfaces, and the tabs are extensions of two of said side surfaces.

3. A metal ladder having a pair of stiles and interconnecting rungs, each stile has a pair of spaced parallel ribs on both its inner and outer surfaces, preferably aligned with each other, and each rung has flat opposite side surfaces which abut against the inwardly facing ribs, and tabs which pass through apertures in the stiles and are bent over the outwardly facing ribs. 5

4. A metal ladder according to claim 3, in which the cross section of each rung is a hollow parallelogram. 

1. A metal ladder including a pair of stiles, and interconnecting rungs, in which each stile has a pair of spaced ribs on its outer surface, and is formed with an elongated aperture adjacent each rib at the position of each rung, and each rung has a pair of tabs at each end which extend through the respective apertures and are bent back over the adjacent rib.
 2. A metal ladder according to claim 1, in which each rung is of hollow box section with substantially flat opposed side surfaces, and the tabs are extensions of two of said side surfaces.
 3. A metal ladder having a pair of stiles and interconnecting rungs, each stile has a pair of spaced parallel ribs on both its inner and outer surfaces, preferably aligned with each other, and each rung has flat opposite side surfaces which abut against the inwardly facing ribs, and tabs which pass through apertures in the stiles and are bent over the outwardly facing ribs.
 4. A metal ladder according to claim 3, in which the cross section of each rung is a hollow parallelogram. 